Method

Toast or grill muffins until golden; spread each half with 1/2 tsp mustard. Divide avocados and pancetta over top of each.

Meanwhile, in deep skillet, heat 2 to 3 inches (5 to 8 cm) water over medium heat until simmering. Stir in vinegar. One at a time, crack eggs into small cup; gently slide into simmering water. Reduce heat to low; cook until whites are set but yolks are still runny, about 3 minutes. With slotted spoon, transfer to paper towel–lined tray to drain.